The broad, long-term goal of this application is to discover and develop pharmacotherapies for the treatment of substance abuse. Since stress can increase drug-taking behavior, we will develop potent and selective ? opioid receptor antagonists as potential new pharmacotherapies to help addicts not relapse to drug taking. Importantly, compounds developed will also serve as biochemical and pharmacological probes useful in gaining a better understanding of the biochemical and molecular mechanisms of cocaine, methamphetamine, nicotine, alcohol, and opiate addictions. Significant research findings directed toward the specific aims of the current grant were achieved. Our progress to date has led to the identification of several compounds that are potent and selective : opioid receptor antagonists in in vitro efficacy assays. The compounds are small molecules that are expected to penetrate the CNS and have high stability. Thus, these compounds are highly useful lead structures that require further development in pharmacokinetic (PK) and animal behavioral studies before their merit as potential pharmacotherapies for treating substance abuse can be determined. The proposed research continues to be based on the original hypothesis that pharmacotherapies for treating substance abuse can be discovered and developed through lead optimization of novel compounds from the : opioid receptor research area. Our general approach will be to design and synthesize compounds based on the (a) trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine, (b) 42- and 92-methyl-5-(3-hydroxy- phenyl)morphan, (c) 4a-(3-hydroxyphenyl)-8a-methyldecahydroisoquinoline, (d) 3-[4-(substituted piperazin-1- yl)]phenol, and (e) N-substituted 4-(3-hydroxyphenyl)-4-methylazabicyclo[3.1.0]hexane classes of opioid antagonist. The merit of the compounds as potent and selective ? opioid antagonists will be obtained by monitoring the ability of the test compounds to inhibit stimulated [35S]GTP3S binding produced by selective , d, and ? agonists using cloned human opioid receptors expressed in CHO cells. Analogs meeting set criteria for ? potency and selectivity will be evaluated in an in vivo PK study to determine the ability of the compounds to cross the blood-brain barrier (BBB) and to have an appropriate half-life (t1/2). Compounds that have high potency and selectivity for ? opioid receptors and that have suitable brain levels and t1/2 values in the PK studies will be evaluated for their ability to antagonize ? selective agonist U50,488-induced diuresis in rats in order to establish their ? opioid receptor antagonist profile (potency and duration of action relative to JDTic). Information generated will be used to select compounds for evaluation in a foot-shock-induced reinstatement of responding for cocaine relapse test. Compounds that show AD50 values in this test comparable to the AD50 of the ? opioid antagonist JDTic, which is in preclinical development, will warrant further development.